1. Field of the Invention
The present invention is broadly concerned with improved flexible teat cup inflations or liners used in automatic milking machines. More particularly, it is concerned with such teat cup liners which are specially designed to provide a differential resistance to inward collapse along the length of the teat-receiving region of the barrel of the liner; a maximum resistance to inward collapse is provided in the portion of the barrel adjacent the mouthpiece of the liner, which resistance gradually and progressively decreases along the axial length of the teat-receiving region. In this way, teats of varying lengths can be properly accommodated without fear of teat damage or chapping as a result of an improperly sized liner.
2. Description of the Prior Art
Conventional automatic milking machines utilize teat cup assemblies including a hollow, rigid outer shell or cup adapted to be attached to a pulsating vacuum line, with an elongated, flexible, resilient, tubular inflation or liner inserted within the shell and extending axially along the length thereof and coupled with a constant vacuum source. Typically, the liner includes an uppermost mouthpiece, a barrel including a teat-receiving region therein, and a short milk tube which extends downwardly to a milk claw for collecting milk from a plurality of teats. The mouthpiece and the end of the barrel adjacent the short milk tube make sealing engagement with the shell to form an annular vacuum chamber surrounding the barrel between the shell and liner. The pressure in this annular chamber is alternated between subatmospheric pressure and a higher pressure, typically atmospheric, by means of a pulsating vacuum line attached to the shell. The constant vacuum line connected via a milking claw to the normally lowermost short milk tube of the liner draws milk from the cow's teat. The interior of the liner is thus maintained at constant subatmospheric pressure, while the alternating pressure conditions in the annular chamber periodically cause inward collapse of the barrel wall of the liner, resulting in a massaging action on the teat. In addition, this periodic inward collapse of the barrel wall intermittently relieves the teat from exposure to the constant vacuum coupled with the lower end of the liner.
It is important that the upper portion or teat-receiving region of the liner grip the teat firmly to prevent vacuum loss and disengagement of the teat cup assembly from the teat. It is also well known that the teats of different cows vary considerably in diameter and length. Changes in teat sizes also occurs during the milking process. These variations in size make it very difficult to produce universal teat cup liners which can be used for milking of a wide variety of cows. This problem also accounts for the fact that a very large number of liner designs have been proposed in the past. Unfortunately, these designs have all been deficient in one or more respects, and the goal of a truly universal liner has heretofore eluded workers in the art.
A principal difficulty in producing a universal liner stems from the fact that virtually all prior designs are constructed so as to collapse at a predetermined intermediate region along the length of the barrel. While such a design may accommodate certain sizes of teats, cows having longer teats cannot properly be milked with these liners. Any attempt to use an improperly sized liner may lead to excessive teat cup crawl during milking, teat chapping and a tendency to induce mastitis.
U.S. Pat. No. 3,289,634 discloses a teat cup liner having upper and lower barrel sections of differential thickness, with the upper portion of the barrel being thicker. An abrupt step or shoulder is provided between the upper and lower regions of the liner barrel, which insures that collapse occurs at the lower, thinner region of the barrel. However, this design cannot properly accommodate teats of varying length. That is, while the design may be satisfactory for use on cows having teat lengths corresponding to the predetermined design, it may be totally useless or even damaging when used on cows having longer teats. Furthermore, this design is deficient in that it does not efficiently accommodate teat lengthening during the milking process. Similar constructions are described in U.S. Pat. Nos. 3,096,740 and 4,269, 143. In both of these patents, use is made of an externally applied sleeve disposed about the liner barrel. Each construction also includes a lower radial shoulder which engages the lower margins of the external sleeves, thereby insuring inward collapse of the liners at predetermined locations.
There is accordingly a decided need in the art for an improved teat cup liner which can properly receive teats of varying lengths, both initially and during the milking process, in order to permit efficient milking of a wide variety of cows while avoiding the problems inherent in improperly fitted teat cup liners.